Rotating grinders



April 968 L. J. B. BEUDIN 3,380,670

I INVENTOR LEUNEL LOU/6 JEAN BAPTJSTE BEUDIN April 1968 L. J B. BEUDIN 3,

ROTATING GRINDERS Filed July 23, 1964 2 Sheets-Sheet 2 INVENTOR LEO/VEL LOU/5 JEAN BAPT'I5'TE BENIN BY M g) ATTORNEY United States Patent 2 Claims. 61.24141 ABSTRACT OF THE DISCLOSURE The invention is concerned with a rotating grinder comprising a drum inside which are provided grinding bars resting upon the inner wall of said drum. The wall of the drum is provided with passages of a radial depth at least equal to the maximum dimension of the grains of material to be ground, the length of the passage in the direction of the drum being smaller than the axial length of the drum. Said passages communicate freely with the inside of the drum but at their outer ends they are provided with screens to prevent the outflow of the material grains not yet ground.

This invention relates to grinders and more particularly to rotating grinders utilizing a hollow cylinder.

The present invention is directed to grinders of the type comprising a rotatable cylinder having a substantially horizontal axis and containing freely rotatable bodies adapted to crush, between themselves and the interior longitudinal wall of said cylinder, products introduced into the latter. This invention is particularly directed to grinders of this type in which the freely rotatable bodies are in the shape of cylindrical bars; but this is only because such a shape seems to have the most valuable applications at present and it should not be treated as limiting the scope of the present invention.

It is one object of the present invention to increase the efiiciency of grinding operations.

It is another object of this invention to eliminate overgrinding, i.e. to insure that the dimensions of at least a majority of the ground particles be above a certain limit.

The embodiments of the present invention involve, principally, the provision, in the longitudinal cylinder wall, of pockets having a depth which is at least equal to the maximum size of the particles which are to undergo the grinding operation or, when the grinding bodies are spherical, the depth preferably being equal to this maximum size plus the depth to which these grinding bodies can penetrate into the pockets, with the result that when these particles rest in the pockets, they can not be crushed or packed down, but will be carried along and later released by the pockets at a point where they will fall ahead (in the sense of the direction of rotation of the grinding bodies) of at least some of said bodies.

The present invention also involves several secondary features which are preferably used together with the principal structure described above and which will be described in greater detail below.

The present invention is directed toward certain modes of application and of construction of the above-described structure and more particularly to grinding devices employing the above-mentioned features, as well as toward elements and tools required for their construction.

These and other objects, features and characteristics of the present invention will become more readily apparent from the following detailed description when considered in conjunction with the attached drawings in which:

FIG. 1 shows a side view of a bar-type grinder representing a preferred embodiment of the present invention;

FIG. 2 is a partly cut-away end view of the right end of the device of FIG. 1;

FIG. 3 is an end view of the left end of the device of FIG. 1; and

FIG. 4 shows a partial end view, similar to the view of FIG. 2, showing, for purposes of comparison, a bartype grinder according to the prior art.

FIG. 1 shows an overall view of a grinder assembly constructed according to the present invention and com prising a hollow rotatable cylinder I intended to receive the material to be ground and containing a plurality of bars capable of freely rolling along the inner cylindrical surface of member 1, the dimensions of the cylinder and the bars, as well as the number of bars and the weight of each, being determined according to the nature of the product treated and desired output rate for the assembly.

Cylinder 1 is supported upon two pairs of friction rollers 3 and 4 so that its axis XX is substantially horizontal, each pair of rollers being mounted on a respective axle 5 which is parallel to the cylinder axis, and the two axles 5 being symmetrically disposed on opposite sides of said cylinder axis. To drive cylinder 1 into rotation about its axis, the rollers 3 are driven, through the intermediary of their common axle 5 and a speed reducer 6, by a motor 7. Rollers 4 can be freely mounted on their axle 5. Each of the rollers 3 being in the same plane perpendicular to the cylinder axis as a respective roller 4, the rollers can be disposed to a pair of circumferential grooves 8 on the outer cylindrical surface of cylinder 1 in order to prevent any displacement of the cylinder along its axis.

According to one variation of the above described structure, the rollers 3 could, like the rollers 4, be mounted for free rotation with respect to their axle 5 and the cylinder 1 could be rotated by a toothed ring gear rigidly mounted to said cylinder, and coaxial therewith, and engaged by a pinion driven by motor 7.

According to still another variation, instead of being mounted on rollers 3 and 4, cylinder 1 could be mounted on a coaxial shaft supported by suitable bearings and driven, through a speed reducer, by motor 7.

As a last step, means are provided for permitting the loading of the cylinder with material to be ground. Such means could consist of a door 9 constituting one of the bases of cylinder 1, for permitting a discontinuous loading, or they could consist of a small chute, for example, or similar arrangement for permitting the continuous introduction of material through an opening arranged in one of the bases. The other base of cylinder 1 is designated as 13 in FIGS. 1 and 3.

Referring to FIG. 2, it should first be noted that, in such an apparatus, at least a portion of the product to be ground, as well as the grinding bars 2, moves to the lower region of the cylinder and that the rotation of the latter (in the direction of arrow F) induces a rotation of the bars (in the direction of arrows 1) due to their contact with the interior surface of the longitudinal wall 10 of cylinder 1. The product to be ground is thus crushed between bars 2 and surface 1011.

Before proceeding with the description of the remaining elements of the apparatus shown in FIGS. 1 to 3,

it would be Well to review briefly the structure and characteristics of comparable prior art grinders. FIG. 4 shows a segment of such prior device in which the interior longitudinal wall 10b of cylinder 10 is completely even and cylindrical with the result that the bars 2 are in contact with this surface over their entire length. The product undergoing grinding accumulates behind the bars 2, taken in the sense of the relative movement of the bars along the surface 10b, which relative movement is in the opposite direction from arrow F. These conditions produce the results, on the one hand, of removing from the grinding operation the product accumulated in region A, behind the zone of action of bars 2, and, on the other hand, of substantially preventing at least the first bar (to the right of FIG. 4) from participating in the grinding operation, since it only encounters a very small quantity of the product (region B).

Returning now to FIGS. 1 and 2, the present invention seeks to remedy the first shortcoming noted above by the provision of pockets 14 in the longitudinal cylinder wall 10. The depth a of these pockets, with respect to surface a, is at least equal to the maximum size (diameter) of the grains of the product to be ground. It should be appreciated that the relative magnitude of dimension a is exaggerated in FIG. 2 for purposes of illustration.

This depth for the pockets permits them to carry some of the product along with them and to later release the product so that it will fall ahead of at least some of the bars, as is indicated in FIG. 2. Some of the product will also fall on the bars and will be carried by their rotation, to their front. It should, of course, be appreciated that the width b of these pockets, taken in the sense of the circumference of the cylinder, must be at least as great as the depth a. Because of the depth of these pockets, the grinding operation is eifectuated only along the cylindrical surface 10a, and not in pockets 14, so that the grains of the product will not be packed down in these pockets and can thus easily fall out of them when the pockets have rotated far enough to begin to tilt, as is indicated schematically in FIG. 2.

The prior art devices present another drawback in that the ground products remain in the grinder until the end of the grinding operation, at which time the cylinder is stopped and all of the product is taken out at one time by way of a door 9, for example. In general, such a procedure produces an over-grinding which is often undesirable. In order to overcome this drawback, the present invention contemplates the provision, at the base of each pocket 14, of a plurality of outlet holes for the ground product. These holes are preferably constituted by the passages in each screen or grating 11 placed in the openings 12 formed in wall 10, the pockets 14 being thus defined by the edges of opening 12 and by gratings 11. These openings 12 are desirably distributed in one of several echelons along the length of wall 10 in such a way that at least one opening 12 will be cut by any plane through the cylinder, perpendicular to the cylinder axis.

In the embodiment shown herein, in which the cylinder rests on rollers 3 and 4, through the intermediary of the solid rims 8, the latter members are located beyond the respective cylinder bases or doors 9 and 13.

The number of pockets 14 is determined experimentally according to the nature of the product to be ground, and the dimensions of the passages in gratings 11 are determined according to the final desired product grain size. Similarly the ratio between the surface area of longtudinal wall 10 and the total surface area of openings 12 is determined experimentally according to the characteristics of the apparatus, e.g. ratio of cylinder length to diameter, rotating speed, and the nature of the product to be ground.

The gratings 11 could be held, by means of screws or similar means, between a flange '15 and the outer cylinder wall, and a shim or wedge 16 may, if desired, be interposed between the grating and the cylinder wall. The wedge 16 and flange each have an opening formed therein which conforms to the shape of opening 12 and which is aligned therewith. By a proper choice of the thickness of shim 16, one can easily give the depth a of the pockets any desired value.

In the case where the bars 2 are replaced by spherical grinding bodies, it is necessary to take into account the depth to which these balls can penetrate into pockets 14 in determining the desired value for the depth a. In this case, a should be at least equal to the sum of this penetration depth and the maximum grain size of the product to be ground.

It thus results that a grinder is obtained from which the grains of the ground product are continuously and automatically removed as they obtain the desired fine ness, with the result that the over-grinding common to the prior art is eliminated.

In order to give a better indication of the improvement which the present invention yields over the prior art, the results of a series of tests on prior art grinders (of the type shown in FIG. 4) and on representative embodiments of the present invention are given below. Examples Nos. 1 and 2 represent grinders according to the invention, while Nos. 3 and 4 correspond to prior art types.

The cylinders used all had the following approximate dimensions in common:

Cylinder comprising 32 rectangular openings, mm. longx25 mm. wide, furnished with metallic screens.

Total useable screened surface dm. 12.8

EXAMPLE 2 Cylinder similar to that of Example 1, with the exception that the surface contains 32 pockets, 160 mm. long x 25 mm. wide x 5 mm. deep, furnished with solid bottoms.

EXAMPLE 3 Sheet metal cylinder having a thickness of 1 mm. and having its cylindrical surface pierced by 'a series of round holes.

Diameter of holes mm 1 Separation between hole axes mm 2 Area of surface perforated dm. 34.7

45% of which is occupied by holes.

EXAMPLE 4 Solid cylinder having a smooth longitudinal wall.

In each test the performance of the grinder is judged on the basis of a load of 1 kg. of siliceous gravel having a grain size which varies between 1 and 2.5 mm.

(a) Comparison between the prior art device of Example No. 4 and the device according to the present invention according to Example 2.

In the test, the device of Example 4 was rotated at a speed of 20 to 30 r.p.m., this being the speed range used for each test. It was noted that the product in this grinder is dragged along by the rotating cylinder wall through an angle of about 100, with respect to a vertical plane through the cylinder axis, and then falls back into the region behind the bars (region A of FIG. 4), thus escaping the region of maximum grinding action and, in particular, the region of action of the first two bars.

The device of Example 2 was rotated at the same speed as the above device. The ground product was carried along by the pocket through an angle of and then fell ahead of the bars, with the result that all of the bars played an active role in the grinding operation.

Results of tests Speed of cylinder rotation 23 rpm.

TEST A Grinder bodies 4 bars, each having a diameter of 50 mm. and a weight of 8 kg, Duration of each run 2 minutes.

Weight of product ground to a grain size of less than 1 In each of the above tests it may be seen that the presence of the pockets more than doubled the grinder output.

(in) For this second series of tests, the cylinder of Example 1 was compared with that of Example 4. The metallic screens were made of wires having a diameter of 0.4 mm. and the space between wires was 0.99 mm.

Results of tests TEST B Grinder bodies 4 bars, each having a diameter of 50 mm. Speed of cylinder rotation 23 rpm.

Time required to reduce all of the product treated to grains of less than 1 mm.:

Example 4 11 minutes 10 sec.

Example 1 2 min. 50 sec.

The screen covered openings serve to reduce the time of grinder operation to one-fourth of that required when no openings are present.

(c) For the third series of tests, the arrangement of Example 3 was compared with that of Example 1.

Results of tests TEST C Grinder bodies 4 bars, each having a diameter of 50 mm. Speed of cylinder rotation 21 r.p.m. Duration of each run 2 minutes 50 seconds.

Weight of product eliminated through the openings:

Example 3 g 265 Example 1 g 1,000

Thus the cylinder of Example 3 is roughly as inefiicient of the solid cylinder, despite the fact that the perforated cylinder has a larger total perforation area than does the cylinder of Example 1.

While several possible embodiments of the present invention have been shown and described herein, it should be appreciated that many variations would occur to one skilled in the art without departing from the spirit thereof and that the coverage of the present invention should be limited only by the scope of the appended claims.

I claim:

1. An improved grinder for grinding solid, particulated material which comprises,

a rotating cylindrical of substantially horizontal axis provided in its cylindrical wall with openings for the outflow of ground material, and

a multiplicity of rounded grinding elements freely movable inside said drum,

wherein the improvements consist:

in the provision of radial passages starting outwardly from said openings and in unobstructed free communication with the inside of said drum,

in that said openings and said passages starting therefrom are elongated in the axial direction of the drum and of a length in said direction equal to only a por tion of the axial length of said drum, the width of said openings and passages and the depth of said passages being greater than the maximum dimension of the particles of said material,

in that said grinding elements are constituted by cylindrical bars of a length of the same order of magnitude as the inner axial length of said drum, whereby said bars cannot project outwardly into said passages beyond the inner wall of said drum, and in the provision of a perforated wall covering the outer end of each of said passages.

2. A grinder accordingto claim 1 wherein said perforated wall consists of a screen.

References Cited UNITED STATES PATENTS 11/1924 Herman 24191 5/1925 Barcherdt 241183 X 

